When a coupling socket member is used to connect a trailer to a ball on a towing vehicle, it has been found desirable to lock the coupling socket member to the ball after they are engaged to insure that the trailer does not become disengaged from the towing vehicle. The locking devices which have been used for this purpose in the past ordinarily employ a pivotal ball retainer within the coupling socket member which pivots into engagement with the ball to lock the coupling socket member to the hitch ball. The ball retainer is controlled by a cam lever overlying the coupling socket member. The cam lever is connected to the ball retainer by a latch bolt which passes through the top of the coupling socket member. When the cam lever is pivoted so as to engage the ball with the ball retainer, the cam lever is locked in position to prevent the coupling socket member from becoming disengaged from the ball.
In certain of the locking devices discussed above, the lock includes a locking latch having a hook which engages the coupling socket member when the cam lever is moved to its locking position. The locking latch can be manually actuated to release the hook so that the cam lever can be pivoted back to its release position. In other such devices, the lock comprises a notch on the latch bolt, and a secondary lever which engages the notch when the cam lever is in the locking position. In these latter devices the secondary lever is actuated to release the lock.
In the devices described above which employ a locking latch that engages with the coupling socket member to lock the cam lever in position, the locking action is not as positive as desired. The hook can become disengaged from the coupling socket member, particularly when the towing vehicle operates on rough roads. In such circumstances the ball rattles against the ball retainer and the coupling socket member and the hook may come loose. Unlocking of the device in this situation is quite critical because on such rough terrain the chances of the coupling socket member becoming disengaged from the ball are substantial, and the tendency of such locking devices to release when they are most needed is quite undesirable. Devices of this type are usually provided with registering apertures in the cam lever and latch bolt through whcih a pin can be inserted to lock the cam lever in position, but the user often neglects to insert the pin or it is lost and the device can still become inadvertently disengaged.
The devices known in the art which employ a notch on the latch bolt and a secondary lever which engages the notch have been found to provide a relatively positive locking action. However, with such devices it is often quite difficult to disengage the secondary lever from the notch in the latch bolt so that the locking mechanism can be released. Such devices cannot be as conveniently unlocked as the trigger type devices can be, discouraging the use of such devices.